add contribution.md guidance
add contribution.md guidance

Signed-off-by: allencloud <36603fc76d0c5a59db517817381acc1be27b9499@daocloud.io>

DaoCloud/daochain,hainesc/daochain,DaoCloud/dao-chain,hainesc/daochain,Revolution1/daochain,DaoCloud/dao-chain,hainesc/daochain,Revolution1/daochain,DaoCloud/daochain,Revolution1/daochain,DaoCloud/daochain,hainesc/daochain,DaoCloud/dao-chain,DaoCloud/dao-chain,Revolution1/daochain,DaoCloud/daochain